Added sum_batches to rnnlm-batch
Added sum_batches to rnnlm-batch

Abasyoni/dynet,cherryc/dynet,cherryc/dynet,kamigaito/cnn,dhgarrette/cnn,Peilun-Li/dynet,cherryc/dynet,kamigaito/cnn,Peilun-Li/dynet,Abasyoni/dynet,mitchellstern/dynet,dhgarrette/cnn,Abasyoni/dynet,Peilun-Li/dynet,mitchellstern/dynet,dhgarrette/cnn